I found them very effective. But I don't ask people to pay, I ask for feedback. If the software is good, they'll want to use it anyway!
People are willing to help if you are equally open about what the software can and cannot do. I implemented several features straight out of what people said they wanted through email, and the product was noticeably better for it.
I've also had people not respond at all or react strangely.
Besides challenging the mind over matter, this work also challenges the idea of what to believe and pursue when scientific evidence is relatively lacking.
Does this mean an actual truck, a vehicle? Did they accidentally hurt someone?
I liked this quote: The future for the dark side looks bright.